修改更新源：
sudo vim /etc/apt/sources.list
删除里面所有内容
方法1: 按ggdG 方法2: :%d
替换源
搜狐源：
deb http://mirrors.sohu.com/ubuntu/ vivid main restricted universe multiverse deb http://mirrors.sohu.com/ubuntu/ vivid-security main restricted universe multiverse deb http://mirrors.sohu.com/ubuntu/ vivid-updates main restricted universe multiverse deb http://mirrors.sohu.com/ubuntu/ vivid-proposed main restricted universe multiverse deb http://mirrors.sohu.com/ubuntu/ vivid-backports main restricted universe multiverse deb-src http://mirrors.sohu.com/ubuntu/ vivid main restricted universe multiverse deb-src http://mirrors.sohu.com/ubuntu/ vivid-security main restricted universe multiverse deb-src http://mirrors.sohu.com/ubuntu/ vivid-updates main restricted universe multiverse deb-src http://mirrors.sohu.com/ubuntu/ vivid-proposed main restricted universe multiverse deb-src http://mirrors.sohu.com/ubuntu/ vivid-backports main restricted universe multiverse
阿里云源：
deb http://mirrors.aliyun.com/ubuntu/ vivid main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ vivid-security main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ vivid-updates main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ vivid-proposed main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ vivid-backports main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ vivid main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ vivid-security main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ vivid-updates main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ vivid-proposed main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ vivid-backports main restricted universe multiverse
网易源：
deb http://mirrors.163.com/ubuntu/ vivid main restricted universe multiverse deb http://mirrors.163.com/ubuntu/ vivid-security main restricted universe multiverse deb http://mirrors.163.com/ubuntu/ vivid-updates main restricted universe multiverse deb http://mirrors.163.com/ubuntu/ vivid-proposed main restricted universe multiverse deb http://mirrors.163.com/ubuntu/ vivid-backports main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ vivid main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ vivid-security main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ vivid-updates main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ vivid-proposed main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ vivid-backports main restricted universe multiverse
保存退出，执行一次更新
sudo apt-get update